division. This undoubtedly terminates in a myelinic nerve-
fibre. The base of the cell is not square, but crenated and
notched by the giving off of numerous delicate basal processes
which are lost in the granular matrix.
The cells all have nuclei and nucleoli, most of which are
round, but some of which seem also to have a triangular shape
corresponding to the cell-body. The cells average 25 /*. in
diameter. A great difference is made in the apparent shape of
the cell by obliquity of the section. If the line of section is
moderately oblique, it shortens the cells ; if still more oblique,
it makes them very short and blunt ; while if the section is at
right angles to their axis, all the cells appear round and of
various sizes. In the deepest parts of this layer the giant-cells
gradually disappear, and the gray matter of the cortex merges
into the white matter. In the two inner layers of the cortex
there are seen many fibres and bundles of fibres having a ver-
tical direction, which, with the blood-vessels (the largest of
which being perpendicular to the surface), give the cortex a
somewhat striated appearance.
We see, then, that the only difference between the second
and third layers of the cortex is the greater number of small
cells in the second and the greater number of large cells in the
third, while the division of the third layer into three, as is
accepted by most authors, seems purely arbitrary, there being
a gradual gradation into the white substance.
Some writers l lay much, stress on the difference of structure
of the cortex in different regions of the hemisphere. It is true
that, in the non-excitable or sensory regions, the cortex is thin-
ner and perhaps less highly organized ; but here are met the
same elements as form the cortex in the motor region (centre,
for the arm, for instance). (See Fig. 150.) Even the giant-cells
are found less numerously than in the motor regions. Another
fact demands attention, that is, that the structure of the cortex
is the same at the bottom of a fissure as on the surface of a
convolution, and for this reason lesions of the sides and bottom
of fissures should receive as much attention as those of the
surface of the convolutions, implicating, as they do, equally im-
CLARKE, J. L. Researches into the Structure of the Spinal Cord. Philosoph.
BONDERS, F. C. Dissertatio anatomica inauguralis de cerebri et medullae spinalis
systeraata vasorum capillari in statu sano et morboso. 1853.
JACUBOWITSCH, N. Mittheilungen iiber die f einere Structur des Gehirns und Riicken-
marks. Breslau, 1857.
JACUBOWITSCH, N. Further Researches into, etc. Breslau, 1858.
BIDDER, F., und KUPFFER, C. Untersuchungen iiber die Textur des Riickenmarks,
etc. Leipzig, 1859.
VAN DER KOLK, SCHROEDER. Minute Structure and Functions of the Spinal Cord
and Medulla Oblongata, and on the Proximate Cause and Rational Treatment
of Epilepsy. New Sydenham Society. London, 1859.
STILLING, B. Neue Untersuchungen iieber den Bau des Ruckenmarks. Cassel,
LUYS, J. Recherches sur le systeme nerveux cerebro-spinal ; sa structure, sea fonc-
tions et ses maladies. Paris, 1865.
His, W. Zum Lymphsystem. Leipzig, 1865.
HIRSCHFELD, LuDOVic. Traite et iconographie du systeme nerveux et des organes
des sens de 1'homme. Paris, 1866.
JOLLY, F. Ueber die Ganglienzellen des Ruckenmarks. Miinchen, 1866.
KOLLIKER, A. i&lements d'histologie humaine. Traduit par Marc See. Paris,
1 See Betz : Anatomischer Nachweis zweier Gehirncentra. Centralblatt f iir die
Medicinischen Wissenschaften, August 1 and 8, 1874, pp. 578 and 595. He finds
" nests " of enormous cells in the motor area, especially of the paracentral lobule.
326 MANUAL OF HISTOLOGY.
HENLE, J. Handbuch der Nervenlehre des menschen. Braunschweig, 1871.
GEULACII, J. The Spinal Cord. Translated by Dr. E. C. Seguin, in Strieker's His-
ScnULTZE, MAX. The General Character of the Structures Composing the Nervous
Substance. Translated by Henry Power. Strieker's Histology. 1872.
RETZIUS, GUST, och KEY, AXEL. Studier i nervsystemets anatomi. Stockholm,
ERB, W. H. Diseases of the Spinal Cord and Medulla Oblongata (Anatomical Intro-
duction). Ziemssen's Cyclopaedia of Medicine. Vol. XIII. American Edi-
SEGUIN, E. C. Lectures on the Localization of Spinal and Cerebral Diseases. N. Y.
Medical Record. 1878.
FORT, J. A. Lemons sur les centres nerveux. Paris, 1878.
HUGUENIN, G. Anatomie des centres nerveux. Traduit par Dr. Th. Keller.
BERLIN, RUDOLF. Beitrag zur Structurlehre des Grosshirnwindungen. Erlangen,
KUPFFER, GUST. De cornus ammonis textura. Dorpat, 1859.
CLARKE, J. L. Researches on the Intimate Structure of the Brain, Human and
Comparative. 1857 and 1867.
ARNDT, RUDOLF. Studien iiber die Architektonik der Grosshirnrinde des Men-
schen. Bonn, 1867-68.
JENSEN, JULIUS. Die Furchen und Windungen der menschlichen Grosshirn Hemis-
pharen. Berlin, 1870.
MEYNERT, T. The Brain of Mammals. Strieker's Histology. Am. edition. New
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BENEDIKT, MORIZ. Anatomische Studien an Verbrecher-Gehirnen. Wien, 1879.
BOYER, H. DE. Etudes topographiques sur les lesions corticales des hemispheres
cerebraux. Paris, 1879.
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BY C. H. WILLIAMS, M.D., BOSTON, MASS.
THE eyelids are very complicated structures. Their exter-
nal coating is formed of skin, which is modified for the special
purpose it has to serve in this situation. Beneath the skin is a
loose sheet of connective tissue ; still more internally is the lit-
tle orbicular is palpebrarum muscle ; behind this again is loose
connective tissue, which shades off gradually into the tarsus.
This latter is not formed of cartilage, as was formerly sup-
posed, but of dense fibrous tissue. The conjunctiva tarsi
lines the inner surface of the tarsus. The skin of the lids
exhibits the usual layers of horny, serrated, and cylindrical
epithelium. At the upper portions the papillae are sparsely
developed and short, but they gradually increase in size and
number as they approach the free edges. A peculiarity of this
skin are the pigment-cells, which are scattered throughout the
cutis. They are more abundant in brunettes than in blondes.
At the confronting margins of the lids are found the cilia
or eyelashes, which resemble the ordinary larger hairs in their
formation and mode of growth ; they are placed in two or
three rows, are well supplied with pigment, and have a definite
direction given to them by the deep follicles from which they
Ordinary sweat-glands are quite numerous, especially in the
upper portions of the lid ; at the lower border we occasionally
find them in a modified form, opening into sebaceous follicles
near or just behind the cilia ; they have a long and wide ori-
fice, and the tubules are filled with fine granular matter, con-
taining occasional roundish masses resembling particles of
Beneath the cutis is a loose connective-tissue layer through
THE EYE. 329
which numerous blood-vessels and nerves pass ; behind this,
and covering the whole extent of the lid, are bundles of the
orbicularis palpebrarum ; some small fasciculi of this muscle
are also found at the lower and inner angle of the lid, enclosing
the openings of the Meibomian glands. These bundles, known
as the musculus ciliaris Riolani, have fibres which are among
the smallest of the striped variety of muscular tissue.
Behind this layer is a thin sheet of loose connective tissue,
which merges without any sharp boundary line into the tar-
sus ; this latter body forms a leaf-shaped plate about twenty
millimetres in length by one millimetre in thickness, and is
composed of very dense connective-tissue fibres separated only
by minute lymph-spaces ; it has few blood-vessels or nerves,
and serves to give the requisite stiffness to the looser tissues of
The Meibomian glands are imbedded in the tarsus. Their
excretory ducts, which are directed at right angles to the pal-
pebral margin, have their openings on the surface of the lid
near its posterior angle. They are lined with epithelium, which
at the external orifice is similar to that in the superficial parts
of the skin ; more internally it is serrated, while in the acini of
the gland it has a cuboidal shape. These glands have a straight
central tube, around which the acini are clustered, and into
which they discharge the sebum, a material composed of epi-
thelial cells that have undergone fatty degeneration. This
oleaginous substance serves to moisten the edges of the lid and
to prevent the overflow of tears.
Above the Meibomian glands, and in part imbedded in the
tarsus, are the acinous glands, which have their openings on
the surface of the conjunctiva fornicis. Above these glands
the smooth muscular fibres of the little palpebralis muscle of
Muller are inserted, through a tendon, into the upper part of
the tarsus ; the fibres of this muscle are quite large and have
peculiar irregular cells with pigmented nuclei scattered
To prepare sections from the lids they should be pinned fiat
on a piece of cork and then immersed in Muller' s fluid' for
eight days. After being washed in water they are placed in
absolute alcohol until sufficiently hard ; or they may be hard-
1 See chapter on General Methods.
330 MANUAL OF HISTOLOGY.
ened by placing in the ordinary per cent, solution of chloride
of gold. This last method shows very clearly 'the nerves of
the lid and conjunctiva, which take a deep violet or mauve
color. For rapid work the lids may be hardened in a saturated
solution of picric acid. They may then be stained with picro-
carmine or hsematoxylon, and mounted in glycerine or balsam.
(See chapter on General Methods.)
The caruncula lachrymalis is a small, rounded mass of
skin ; it is placed between the lids at their inner angle, and
contains hairs, vessels, and glands, such as are found else-
where in the cutis. Its office is to prevent the overflow of tears.
The conjunctiva. Just behind the tarsus, and separated
from it by a thin layer of fibrillated connective tissue, is the
conjunctiva, which, after lining the inner surface of the lid,
passes backward as a loose connecting fold (fornix) to the
sclera, over which it is reflected forward as far as the margin
of the cornea. The conjunctiva consists of an external or
epithelial layer and a tunica propria or proper investing mem-
brane. There is also a subconjunctival layer.
The lower portion of the conjunctiva, where it takes its
origin from the margin of the lid, is quite smooth ; but near
the upper edge of the tarsus it becomes more or less infiltrated
with lymph- cells, and is thrown into numerous folds, which
have sometimes been mistaken for glands. The epithelial ele-
ments of this part vary much in shape ; in general there are
two layers : a superficial one, composed of cylindrical bodies
which are a continuation of the superficial strata of the skin,
and a deeper one of small, round cells, representing the changed
cylindrical elements of the Malpighian layer or rete mucosum.
The tunica propria consists of fine connective- tissue fibres,
in which a few elastic fibrillse are interspersed. The subcon-
junctival layer resting immediately upon the tarsus is very
thin. That part of the conjunctiva forming the fornix has an
abundant subconjunctival tissue, which is composed of loose
elastic fibres and vessels ; the epithelial layers are also thicker
here, and small racemose glands, supposed to secrete mucus,
are also found there.
On the conjunctiva covering the bulb the epithelium con-
tains here and there the large mucus-cells corresponding to
the goblet- cells of the intestines. It gradually begins to change
its character and passes over into the variety which is seen in
THE EYE. 331
the cornea, and, in fact, is continuous with it. The tunica
propria has an abundant supply of blood-vessels, and is loosely
connected with the sclera by fibres, which become more numer-
ous and firm in the vicinity of the corneal margin.
The nerves of the conjunctiva may be seen by cutting small
pieces of fresh conjunctiva from a pig or calf and examining
them in aqueous humor, or in a 1 per cent, aqueous solution of
common salt care being taken to support the cover-glass at
the sides, in order to avoid pressure. The nerve-fibres can then
be seen passing under the epithelium ; they can be distin-
guished with certainty by their annular constrictions (anneaux
constricteurs) ; after penetrating a short distance, however,
they lose their medullary sheath and form open networks
under the epithelium ; a few fibres find their way toward the
surface between the epithelial cells.
The gold method is of special use in exposing the finer
nerve-branches. The question of the manner in which the
nerves ultimately end is still a point in dispute.
The lymph-spaces of the conjunctiva are quite numerous,
especially near the corneal border ; here they are narrow, and
finally pass forward to unite with the lymph-spaces of the cor-
nea, from which they can be injected by means of a solution
of alkanet-root in turpentine. 1
The normal conjunctiva does not have any true papillae, but
on the tarsal portion the surface often has small papilliform
projections covered with epithelium.
The cornea. This tunic is covered with stratified epithe-
lium (a), comprising layers of flat, serrated, and cylindrical
cells. Directly beneath these is the anterior limiting or Bow-
man's membrane (b) ; this is a clear, homogeneous stratum,
which differs from the substantia propria of the cornea only in
containing no lymph-spaces or cells. It can be divided up
into the same line fibres as the cornea itself, and its inner bor-
der has no distinct limit, the fibres passing directly into the
corneal tissue ; when this layer has been destroyed, as by a
perforating ulcer or wound, it is not regenerated.
The substantia propria of the cornea (&, c) is made up of
lamellae, like the leaves of a book ; these lamellae, which at
first appear homogeneous, can be separated into fine fibres, just
See chapter on General Methods.
MANUAL OF HISTOLOGY.
like other connective-tissue membranes, by dissolving out the
cementing substance in a 10 per cent, solution of common salt.
With the exception of tlivfibrcearcuatce, which curve for-
ward through several strata in the anterior portions of the
cornea, the fibres pursue the same direction as the layers ; but,
although most of the fibres run parallel to the surface of the
cornea, yet they may have a different direction in each layer,
FIG. 151. Meridional section through the cornea of the human adult, from an eye hardened in Mill-
er's fluid. The section was colored with carmine, and made transparent by the oil of cloves.
so that when viewed from above the fibres will appear to cross
one another. This explains the formation of the stellate fig-
ures which are sometimes observed after the injection of fatty
substances into the cornea, or by the infiltration of bacteria
between the fibrils.
In the interfibrillar material are found the lymph- canals
and spaces, which contain the fixed corneal corpuscles (Fig.
152). These spaces are stellate and broad when seen from above,
but thin and spindle-shaped on side view ; they have numer-
ous branches and branchlets given off from them at right
angles (lymphatic channels) (Fig. 152, A). The spaces and
branches usually lie in the plane of the lamellae, anastomose
freely with one another, and are filled with the corneal corpus-
cles and lymph (Fig. 152, B).
In life these fixed bodies nearly fill the lymph-spaces and
conform to their size and shape ; they are flat corpuscles, usu-
ally nucleated, and have short, sharp-pointed processes, which
pass out into the minute lymph-canals. In the lymph-spaces
of the cornea are also found, even in normal conditions, a few
migratory cells, resembling white blood-corpuscles ; they are
very numerous when the cornea has been irritated, and can
be seen in a frog's cornea, which
has been kept five to fifteen
minutes in serum or aqueous
humor in a moist chamber, and
examined without pressure on
a warm slide.
Beneath the subs tan tia pro-
pria of the cornea we find the
posterior limiting layer, or
Descemef s membrane (d) (Fig.
151). This is transparent, ap-
parently homogeneous, rolls up
when cut, is intimately connect-
ed with the posterior fibres of
the cornea proper, and is lined
on its inner surface with endo-
thelium (e). It contains no cel-
lular bodies, but, like the anterior limiting layer, can be sepa-
rated into fibrillse, and appears to represent a concentration of
the corneal fibres rather than a separate structure.
The endothelium is a single layer of flat cells lining the
anterior chamber. Blood-vessels are found only in the normal
cornea at the periphery, where they form a fine network con-
necting with the conjunctival and scleral vessels.
The nerves enter the cornea at the posterior part of the
periphery ; they soon lose their neurilemma and medullary
sheath, and pass forward obliquely, as small axis-cylinders,
toward the epithelial layer ; here they divide up into branch-
lets, often having a ganglionic enlargement at the point of divi-
sion. Under the epithelium these delicate fibres form a net-
work which sends some very minute filaments upward between
the epithelial cells. Their further course is unknown.
To separate the cornea into its constituent fibres, small pieces
should be soaked for twenty-four hours in a concentrated pi-
Fio. 152. -Lymph spaces and canals, A ; fixed
corneal cell, partly filling these spaces, B. After
334 MANUAL OF HISTOLOGY.
eric acid solution ; they can then be washed in water and easily
picked to pieces. In order to see the arrangement of the fibrillse
in the different layers, the cornea of a rabbit should be pricked
with a needle in several places ; then some highly infectious
fluid, as the exudation in puerperal peritonitis, is to be brushed
over the surface, and in a few days an infiltration will have
taken place throughout the interfibrillar substance. We shall
then see the lines of pus-cells crossing one another in different
directions, and sometimes collections of micrococci forming
A very delicate preparation of the fixed corneal cells may
be made by removing a fresh cornea, and then immersing it
from three to six hours in aqueous humor, in a moist chamber.
In examining it take care, as before mentioned, to avoid any
pressure upon the cover-glass.
It is easier, however, to demonstrate the cells and lymph-
spaces by staining with silver or gold. To do this the nictitat-
ing membrane of a live frog should be cut off or held to one
side by an elevator ; the exposed cornea is then placed near the
mouth of a test-tube, in which some water has been raised
to the boiling point ; when the epithelium begins to appear
opaque it should be carefully wiped off with a fine cloth ; a
per cent, aqueous solution of nitrate of silver is then applied ;
when the cornea has become thoroughly white by this method,
it is to be removed, washed in a weak solution of common salt,
placed in distilled water, and exposed to the light until it be-
comes brown. It should then be cut at the edges and mounted
in glycerine. In ten or fifteen minutes it will be transparent
and ready for examination. Instead of removing the epithe-
lium by steam, a solution of silver nitrate (-J- per cent.) may be
used, the lids being held out of the way until the epithelium
appears whitish; this outer layer is then removed, and the
same process repeated as before. The substantia propria as-
sumes a brown color, and the corpuscles appear as lighter spaces
in it. The nuclei may be exposed by hsematoxylon.
The best preparations, both for the lymph-spaces and the
nerves, are made with chloride of gold. A fresh cornea, pref-
erably one from a live pigeon, is removed immediately after
decapitation and immersed for five minutes in lemon- juice,
then washed in distilled water, placed for fifteen minutes in a
1 per cent, solution of chloride of gold, again washed, and this
THE EYE. 335
time soaked for twenty-four hours (well protected from the
light) in a 2 per cent, solution of formic acid. After another
washing in distilled water the cornea should be cut in two and
placed in glycerine ; one portion can then be separated into
thin layers, by tearing with tine forceps or needles.
Examine in glycerine for the corneal corpuscles, nerves,
and lymph-spaces, which latter appear dark on a light blue
or red background ; or the piece may be imbedded in wax or
some such material, and sections made parallel to the surface
of the cornea. The remaining half of the specimen is to be
imbedded or held in liver or pith. Transverse sections may
then be made. These will exhibit on lucky sections the fine
plexuses of nerve-filaments under the epithelium, with occa-
sional fibres passing up between the individual corpuscles.
The different layers of the cornea will be well shown, also the
narrow corneal cells (as seen on side view), together with the
remains of the endothelial layer on the inner surface.
The peripheral portions of the cornea are particularly inter-
esting. We have here the transitions from cornea to conjunc-
tiva and sclera, the origin of the ciliary muscle, the ligament
of the iris, and the numerous vessels of the part.
The epithelium of the cornea (a) forms a gradual transition
into the epithelium of the conjunctiva, but the anterior limit-
ing membrane (Bowman's) becomes thinner as it approaches
the edge of the cornea, until finally it merges with the fibres
of the anterior corneal layers into the tunica propria of the
No sharp boundary line has been demonstrated between
the cornea and the sclera. Under the microscope the fibres
appear to have no distinct limit ; the lymph-spaces also of the
cornea are continued directly into the sclera, and the scleral
and corneal fixed corpuscles are much the same.
The posterior limiting membrane (DescemeV s] (c), like the
anterior, becomes gradually thinner and loses itself in a small
bundle of scleral fibres which surround the edge of the mem-
brane and form the anterior support to the ligamentum pec-
The endothelium (Fig. 153 6, ) passes uninterruptedly over
this ligament (e f ) and is reflected forward over the anterior sur-
face of the iris (e") to the edge of the pupil.
In the ^ngle between the iris and cornea, forming buttresses,
MANUAL OF HISTOLOGY.
as it were, to hold the iris in position, is the ligament of the
iris (d), composed of loose connective tissue with an abundant
open mesh work, enclosing spaces (Fontantfs spaces), (f), which,
on the one hand, connect with the anterior chamber by small
openings lined with endothelium, and on the other with the
lymph-spaces of the cornea and sclera, as may be shown by
injecting a solution of aniline blue into the anterior chamber.
FIG. 153. Corneal margin from a meridional section of the human eye : a. a', external epithelium of
the cornea ; a', a", epithelium of the conjunctiva bulbi ; 6, &'. &', corneal tissue ; ft 7 , &', &", &", sclerotica ;